This invention relates to a device for interconnecting a series of data acquisition apparatuses to a remote receiving and recording central system.
More particularly the invention concerns a device for interconnecting a series of electronic apparatuses, each of which is adapted to collect analog signals generated by a plurality of signal generators, to convert them to digital signals and to transmit them sequentially to a remote receiving and recording system, this interconnection device having a high transmission capacity.
The interconnection devices of a known type generally comprise one or more data transmission lines onto which can be connected a plurality of electronic data acquisition apparatuses. Each of them is adapted to collect, by sequential sampling, a plurality of analog signals generated by a certain number of generators and to memorize them temporarily. The receiving and recording system is adapted to successively interrogate the different acquisition apparatuses. Upon reception of appropriate control signals, each acquisition apparatus is connected onto the one or more transmission lines in order to transmit the locally collected data to the receiving and recording system.
The interconnection devices of this type are, for example, used in seismic prospecting to transmit to a remote recording system the seismic signals collected from a very large number of sensors or sensor groups distributed along the seismic profile on survey and corresponding to the echoes, on subterranean reflecting surfaces, of seismic signals transmitted intermittently. The sensors or sensor groups are distributed in several assemblies respectively connected to electronic seismic data acquisition devices connected at regular intervals onto the transmission lines. In marine seismic prospecting, particularly, the sensor assemblies are contained in sections of a seismic streamer of great length, towed, while immersed, behind a ship, for example. The acquisition apparatuses of the signals generated by each of the sensor assemblies are also arranged at regular intervals inside the seismic streamer and are connected to a receiving and recording system placed on the towing ship, through one or more transmission lines. The transfer of the seismic signals comprises a first analog multiplexing, effected by each acquisition apparatus for sequentially collecting the seismic signals received by the sensors of each sensor assembly, then a second digital multiplexing effected by the receiving and transmitting system, in order to successively transmit the data collected from the different acquisition apparatuses onto the one or more common transmission lines.
Such an interconnection device is described, for example, in the French patent application E. No. 79/30 287. It comprises two "outward" transmission lines and two "inward" transmission lines serially connecting a plurality of data acquisition apparatuses to a receiving, recording and testing system placed on a towing chip.
The data transmission lines used in practice consist generally of a pair of twisted conductor wires whose transmission capacity is about 2 Megabits/s. This transmission capacity is compatible with the bandwidth of the logic electronic elements (for example of the C MOS type) generally used in the data acquisition apparatuses. However, when increasing the number of interconnected acquisition apparatuses on the same transmission line or lines, the bulk of informations passing therethrough or processed by the electronic elements of these acquisition apparatuses, becomes quickly incompatible with the performances of the currently used equipment. This leads to the requirement of use of transmission lines in the form of coaxial cables and of electronic logic elements of higher performance. As a result the electric consumption and the manufacturing costs are substantially increased.